The invention relates to a system for controlling the pumping capacity of a lubricant pump for an internal-combustion engine.
It is generally known, in the case of internal-combustion engines, to use rigidly driven oil pumps for supplying the oil circulating system, which oil pumps are constructed, for example, as external gear pumps or internal gear pumps or as vane cell pumps. These are oil pumps with a variable or constant delivery volume per pump wheel rotation. So-called constant-delivery pumps are equipped with a pressure limiting valve, by means of which the maximal oil pressure can be adjusted. When the oil pressure limiting valve opens at a maximal oil pressure which is set beforehand, the excess oil volume is returned into the low-pressure part of the oil pump.
Since the oil volume flow required for the lubrication of the engine is not always proportional to the rotational speed of the engine or to the rotational speed of the pump, suggestions have been made that the oil pressure be controlled in order to be able to reduce the driving power of the engine oil pump particularly in the partial load range. Thus, for example, from Japanese Patent Document JP-OS 9-885 33, a system is known for controlling the oil pressure of a gear pump in the case of which a bypass of the gear pump monitored by the pressure regulating valve can be opened or closed as a function of the pressure. For this purpose, the piston head is provided with an opening or throttle which is connected with an interior constructed on the rear side of the piston valve. A control valve is connected in front of the interior of the piston valve, by means of which control valve, the differential pressure existing between the forward and rear side of the piston valve can be changed and therefore the opening oil pressure can be adjusted.
From German Patent Document DE 43 02 610 A1, a vane cell pump is known which has a variable delivery volume and in the case of which the volume flow can be adjusted by a change of the position of the lifting ring with respect to the axis of rotation of the rotor. Furthermore, in addition to the pure maximal oil pressure limitation or of the delivery volume control, an additional limitation of the delivery volume as a function of the temperature and/or the rotational speed of the engine is suggested. For this purpose, high-expenditure temperature-dependent control elements as well as additional pressure control systems are required which, in addition to the maximal oil pressure limitation, cause an adjustment of the lifting ring of the vane cell pump and therefore, as required, a reduction of the delivered oil volume flow.
It is therefore an object of the invention to provide a system for a volume-flow-controlled vane cell pump by means of which a lubricating oil supply of the internal-combustion engine which meets the requirements takes place in a simple manner, so that the taken-up power of the oil pump can be reduced as a result of a lowering of the oil pressure in certain operating conditions.
By means of the suggested system, the driving power required for the lubricating oil supply of the internal-combustion engine in the case of a vane cell pump can be controlled in a simple manner as a function of operating parameters of the internal-combustion engine. As a result, the oil pressures required for the various operating conditions of the engine can be adjusted or adapted, so that another fuel saving potential exists because of the reduced taken-in power in comparison to an uncontrolled oil pump. The suggested system for reducing the oil pressure can be retrofitted in a simple manner in the case of vane cell pumps which are already in operation.
The force directed against the engine oil pressure on the piston rear side of the pressure regulating valve is generated by a flat coil spring which is guided and supported in a receiving opening provided on the rear side of the piston.
For the pressure-dependent controlling of the oil volume flow, a valve element is integrated in a hydraulic pipe leading from the regulating valve to the tank, by way of which regulating valve the oil flow can be adjusted which can be returned to the suction side of the oil pump.
The oil pressure or the oil volume flow delivered by the oil pump is controlled as a function of operating parameters of the internal-combustion engine, such as the rotational speed, the load or the engine oil temperature.